I wrote 3 libraries that can managed little scheduled tasks.
Two of them use interrupts, the third doesnt'.
They are leOS, leOS2, and looper.
leOS uses a microcontroller's timer to launch the tasks at the interval specified by the user.
Tasks have be small and doesn't have to use other interrupt based functions.
leOS2 uses the watchdog timer so it preserves the timers for the user's needs.
It can also be set up with a timeout value, to reset the MCU if a task gets into a neverending loop causing the MCU to freeze. They are not complete RTOS but they are easier to use and good for simple tasks.page on leOS/leOS2thread on this forum
The last one is looper, it is a millis()-based scheduler and it can call simple jobs.page on looper
Glad to give you more info if needed.
PS: thanks, Bob